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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 09-19-2014, 01:43 PM   #21
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Originally Posted by sixshooter View Post
GTX2867R and low boost because you bought the wrong pistons.

Smaller turbos that would spool faster need to make more pressure to achieve the same power but make more heat. You can't handle as much heat because you chose a higher compression piston. Therefore your car will be a slower spooling compromise.

For a serious car, I would use the 2867 at high boost with the lower compression pistons. And if it was track only, i'd consider e85.
They're all serious cars. This is actually going to be my all-around car, for everything from track days to Cars n' Coffee. Anyone who saw me at Laguna Seca probably knows that reliability is WAY higher on my list right now than ultimate horsepower.

So it's a compromise, and I don't actually mind a little boost lag as it's not really an issue at track rpm's, and is more fun than anything on the street. Compromises always mean that someone else's choice is better...for them.

No, we're planning a "serious" track car now that should end up with a 5:1 horsepower to weight ratio, but I'll start a new build thread when that happens.
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Old 09-19-2014, 01:59 PM   #22
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I'd err on the side of a larger turbo than a 2560 if you want a little boost delay on the street. I abslutely loved the whooshiness of my 2876 on my 01. Plus you can run fairly low boost levels and get monster power.

I also have a theory that reducing boost response helps real world MPG but ... no data to back that up.
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Old 09-19-2014, 02:12 PM   #23
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He is actually more of a Rotrex guy.
No surprise. 9.5:1 might be what you want for a low-boost responsive Rotrex. Everyone with any turbo experience understands that 8.6 motors make more torque with a turbo than 9.0 motors because you can run more timing with lower compression, especially on pump gas.

9.5 is the bastard child of compression ratios - not high enough to take advantage of E85, and too high to work well on pump gas. I don't know why Supertech makes that piston, honestly.
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Old 09-19-2014, 02:18 PM   #24
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Originally Posted by 18psi View Post
oh c'mon guys, seriously??!!

gimme a break.

9.5 vs 8.6 and now the engine is next to useless? I realize all the track 1337's look down on us street car peasants, but to go this far is getting ridiculous.
It has nothing to do with track vs. street and everything to do with not pulling a bunch of timing on pump gas. These engines do not like compression, period. Even on NA motors running 11:1+ on 91 octane doesn't get you more power than running 10.5:1 and taking advantage of the extra timing you can get. If you can't get MBT, you left power on the table by running too much static compression.

This is like turbo BP 101, when did everyone suddenly forget that 8.6:1 is good and 9.5:1 is garbage? WTF?
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Old 09-19-2014, 02:41 PM   #25
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Originally Posted by Savington View Post
No surprise. 9.5:1 might be what you want for a low-boost responsive Rotrex. Everyone with any turbo experience understands that 8.6 motors make more torque with a turbo than 9.0 motors because you can run more timing with lower compression, especially on pump gas.

9.5 is the bastard child of compression ratios - not high enough to take advantage of E85, and too high to work well on pump gas. I don't know why Supertech makes that piston, honestly.
For guys like me who are trying to split the baby.
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Old 09-19-2014, 03:55 PM   #26
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You want a piston that will make good power on pump gas and good power on E85, so you picked a piston that does neither of those things?
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Old 09-19-2014, 03:57 PM   #27
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You want a piston that will make good power on pump gas and good power on E85, so you picked a piston that does neither of those things?
OUCH! You are definitely in the running for driest sarcasm on the boards.

No, don't really want to mess with E85 and will run premium only, or race gas at the track. I know, California premium is cat ****.
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